Thursday, 18 November 2010

NASA's WISE infrared space telescope is losing its refrigeration, but its backlog of data is still yielding cool images such this one of an odd, blobby, jellyfish-like nebula.

"I just happened to look up one of my favorite objects in our WISE catalogue and was shocked to see these odd rings," said Michael Ressler, a member of the WISE science team at NASA's Jet Propulsion Lab, in a press release.

The object, called the "Crystal Ball" nebula or NGC1514, is a planetary nebula located 800 light-years away in the constellation Taurus. Planetary nebulas form when a dying star puffs off its outer layers of material and illuminates the gaseous cloud from within. They're called "planetary" because the first such objects discovered were roughly spherical, like a planet, although nebulas with lopsided wings are now known to be common.

"This object has been studied for more than 200 years, but WISE shows us it still has surprises," Ressler said. The observations are reported Nov. 9 in the Astronomical Journal.

The rings could be dust ejected from a pair of dying stars at the nebula's center, one a giant star heavier and hotter than the sun, the other a dense white dwarf. The giant star sheds some outer layers as it ages to form a bubble around the two stars. Jets of material from the white dwarf are thought to have smashed into the bubble, forming the rings that glow orange in the WISE image.

The green cloud is an inner shell of previously shed material, which shows up in light blue in the visible image.

The rings went undetected until WISE because their dust is heated and glows with the infrared light that WISE can detect. In this image, infrared light with a wavelength of 3.4 micrometers is blue; 4.6-micrometer light is turquoise; 12-micrometer light is green and 22-micrometer light is red. In visible-light images, the rings are washed out by the bright clouds of gas.

Many more surprises lurk in the piles of data WISE collected between January and October of this year. The first batch of data will be released to the astronomical community in spring 2011. Meanwhile, WISE — which ran out of coolant in late September and is now too warm for two of its infrared cameras to function — is continuing on as NEOWISE, searching for near-Earth objects like asteroids and comets.

Planetary nebulae with asymmetrical wings of nebulosity are common. But nothing like the newfound rings around NGC 1514 had been seen before. Astronomers say the rings are made of dust ejected by the dying pair of stars at the center of NGC 1514. This burst of dust collided with the walls of a cavity that was already cleared out by stellar winds, forming the rings.

A new crowdsourced science project uses thousands of human eyes to identify stars in their death throes. The first report shows that armchair astronomers can catch a new supernova just hours after the star explodes.

"With very little training, people can spot real supernovae candidates," said astrophysicist Arfon Smith of the University of Oxford. "They're as good as any professional astronomer would expect to be."

Supernovas are the bright bursts from exploding stars that have reached the ends of their lives. These dramatic flares can briefly outshine entire galaxies, but their brilliance quickly fades. A supernova appears to Earth-based observers as an unexpectedly bright star that was not so bright the last time you looked. But other objects, like approaching asteroids and variable stars, can trigger false alarms.

Discriminating software can throw out about 90 percent of the fakes. But the last 10 percent had to be sifted through by humans, who, until about a year ago, were "a small but tiring team of [about eight] PhD students" sorting through up to 5,000 images a night, Smith said.

The new project, Galaxy Zoo Supernovae, takes the work to the masses. Galaxy Zoo Supernovae is an offshoot of the citizen science powerhouse Galaxy Zoo, which began asking at-home volunteers to identify galaxy shapes in 2007 and has since branched out to the moon, solar storms and even historical weather data.

In the supernova project, amateur enthusiasts look through images from the ongoing Palomar Transient Factory survey to sort the dead stars from the living.

Each participant is shown three images of the same region of the sky: one image that the survey telescope just captured an hour ago, a shot from days or weeks earlier, and an image where the "before" shot has been subtracted out and only the supernova candidate remains.

The citizen scientist is then asked a series of three or four questions designed to rule out supernova impostors.

More than 2,500 volunteers sorted through nearly 14,000 supernova candidates between April and July 2010, Smith and colleagues report in a paper submitted to the Monthly Notices of the Royal Astronomical Society. Citizen scientists correctly identified 93 percent of the brightening objects, with no false positives.

The crowd of citizen scientists was also faster at classifying the supernova candidates than the small team of professional astronomers had been.

"All of our candidates get classified within 20 minutes every day," Smith said.

That's exciting for supernova experts, who want to catch and follow up on explosions as quickly as possible.

"The first few hours or days after a supernova explosion reveal information that is crucial to furthering our understanding of what kinds of stars explode and how the explosions occur," said supernova expert Alex Filippenko of the University of California, Berkeley. "Imagine studying an adolescent or an adult; it would help to have photographs, videos and audios of that person as a baby."

Ultimately, though, the Galaxy Zoo crew would like to cut out the human middlemen. The team is using the data collected from Galaxy Zoo Supernovae to train the next generation of supernova identification algorithms.

"It's a feedback loop: classifications from people can help make algorithms stronger in the future," Smith said. "I think if we were still running this project in three years time, I would be disappointed."